The primary distinguishing feature for red-capped leccinums is what tree they are growing with, combined with the color of the scabers and the staining characteristic for the flesh. Those are all helpful indicators.

The primary problem with distinguishing the red-capped leccinums is the fact that the various species are not polite enough to restrict themselves to a particular type of tree even if they have a preference, and will vary both their scaber color and their staining characteristics according to age, environmental effects, and other normal variations within the species.

Thus the indicators cannot be used as actual proof. They just help you establish the odds.

Frustrated yet? Just wait! It gets even more confusing.

First we need to start with a bit of history. In Europe there are several well-defined species: L. aurantiacum, which has red-brown scabers & grows under hardwoods, L. vulpinum, which has black scabers & grows under conifers, L. piceinum, a duller-capped species that grows under spruce, etc. All are excellent edibles that were much desired by the European settlers in North America.

Simply using the European names would have been bad enough, but relatively easy to solve by assigning new ones depending on whether genetic tests proved that any given species could or couldn’t span both sides of the Atlantic. Such was not to be, however.

The settlers did not just import the European names. Instead they used use the single name “aurantiacum” to describe all of the red-capped North American red-caps without regard to what tree they grew with, how they stained, or how the scaber colors might vary. And, indeed, most of the so called “aurantiacum” found in North America was actually growing with some kind of conifer. In other words the only thing we can guarantee is that the mushroom known as L aurantiacum across the Northeast is not the actual aurantiacum from Europe. It may actually be L. vulpinum but even that isn’t clear because the Leccinums have lagged behind badly when it comes to DNA tests.

The bottom line is this: The people who know these things are morally certain that (a) the North American red-capped Leccinums include a spectrum of similar-looking species, (b) pretty much all the names in the field guides will someday have to be changed as those species get better defined, and (c) there are probably some European species mixed in just to keep us all on our toes. Until that gets settled out my solution will be to have the Bolete Filter use the old, known-to-be-improper names as “placeholders” for whatever is going to happen in the future. Here are the basic dividing lines: